Apparatus for producing containers of thermoplastic material

ABSTRACT

Apparatus for blow molding hollow plastic bodies ( 7 ) comprising a plurality of pairs of mutually joinable half-molds ( 2, 4 ) capable of being opened and closed, associated to an appropriate rotary apparatus ( 10 ) carrying said half-molds ( 2, 4 ), a retrieval device adapted to remove the finished container ( 7 ) from the respective pair of half-molds ( 2 ) after the opening thereof, an opening and closing mechanism adapted to close the half-molds ( 2, 4 ) after the passage thereof through the position of the preform feeding mechanism, and to open them before the passage thereof through the position of the finished-container removal mechanism, in which said pairs of half-molds ( 2, 4 ) are constituted by a fixed half-mold ( 2 ) and a moving half-mold ( 4 ) that is capable of being opened from and closed against said fixed half-mold ( 2 ). In a preferred manner, said fixed half-molds ( 2 ) are linked to said rotary apparatus ( 10 ) and are arranged in a substantially vertical position, with the respective moving half-mold ( 4 ) adapted to be closed by accomplishing a substantially rotary movement about a horizontal axis of rotation.

BACKGROUND OF THE INVENTION

The present invention refers to an improved apparatus for the productionof containers made of thermoplastic material, in particular polyethyleneterephthalate (PET) and polypropylene (PP), intended for use inapplications employing them being filled with liquids at elevatedtemperatures and/or containing CO₂ (carbon dioxide) gas, provided withdevices that enable the productivity of moulds during the blow mouldingphase to be increased.

In particular, the present invention is particularly advantageous whenthe described devices are associated with a preform manufacturingapparatus included in a so-called single-stage plant, but can beadvantageously used also in conjunction with apparatuses that aresupplied with previously manufactured preforms and are solely intendedto carry out a final blow moulding phase (ie. two-stage plants).

In a two-phase process, a previously produced preform or parison, whichis in a substantially amorphous state, is heated up again to itspreferred molecular orientation temperature, at which it is thenblow-moulded into the desired shape. As used in this context, the term“two-stage process”, or “double-stage process”, shall be understood tocover any process that produces a preform or parison which must then beheated up from ambient temperature to the related blow-mouldingtemperature.

In contrast therewith, single-stage processes are so defined in thatthey are capable of forming the so-called preform, or parison, andtransferring the preform from the injection mould or extrusion die (uponit having been allowed to cool down to some appropriate temperature) toa conditioning station, where it is allowed to level evenly at atemperature of preferred molecular orientation. The preform or parisonis then transferred to a blow-moulding mould, in which it is finallymoulded into its desired form. According to a prior-art technique, thecavities in which the preforms are injection moulded and the preformtransferring and conditioning devices are arranged in an on-lineconfiguration along with the blow-moulding moulds, so as to ensure aneasier, more convenient handling of the preforms, the containers and thevarious members therewith associated.

According to such a construction principle, both preforms and finishedcontainers are processed in successive groups, with the same processingand/or transferring operations occurring at the same time.

In particular, the blow moulding tools, the the moulds, are particularlycritical in this connection, since with the increasing blow mouldingpressure and the increase in the number of cavities contained in eachpair of blow moulding platens, more rapid and powerful pumping stationsare required. Furthermore, the increased total pressure produced by thebottles during blow moulding must be opposed by a corresponding greatermould clamping pressure.

Such a greater pressure, which can be estimated to amount to a clampingforce exerted on the moulds in excess of 100,000 kgf, would require allmechanical and pneumatic organs intended to produce and withstand such apressure to be sized accordingly, which generally means to a veryburdensome extent.

Such a huge and, what's more, pulsating pressure, however, has anegative effect also on the resistance of the moulds themselves, whichare not only exposed to a greater pressure, but have, at the same time,to be capable of withstanding such pressure over a much greater period,owing to the greater number of blow moulding gates, and this of coursecauses the rigidity thereof to become a critical factor. It also makesit easier for the moulds to warp outwardly, thereby affecting the bottleblow-moulding results in an easily understandable manner.

Furthermore, when use is made of blow moulding moulds provided with alarge number of cavities, the time needed for all preforms to betransferred into the respective cavities increases in a proportionalmanner with a corresponding increase in the cycle time and a resultingreduction in the overall productivity of the plant.

In order to do away with such drawbacks, a largely known solution liesin the replacement of blow moulding moulds provided with a plurality ofon-line cavities with a smaller number of individual moulds, ie.comprising a single respective blow moulding cavity, which are arrangedalong the periphery of a rotating carousel-like structure, such as forinstance illustrated in WO 95/05933, WO 89/01400, U.S. Pat. Nos.4,850,850 and 4,313,720.

In particular, WO 89/01400 teaches that the blow moulding half-mouldsare adapted to open and close in a book-like manner about respectiveaxes of rotation that are orthogonal to the plane on which the preformsand the finished containers move.

Such a solution, although effective in solving the afore cited problems,does not however go without some drawbacks that are summarized below:

a) the need arises for two half-moulds to be handled and driven, andthis, of course, adds to the complexity of the structures and causescosts to rise;

b) the lateral rotary movement of both the half-moulds requires, ofcourse, the availability of adequate lateral space, and this, of course,puts a penalty on the compactness of the plant;

c) the handling means provided must be able to introduce the preformsfrom the front zone of the half-moulds, as well as to again remove therespective finished containers from the same front zone, and this ofcourse understandably adds significantly to the complexity of bothconstruction and operation of the plant.

However, during operating tests carried out on some types of plantshaving the characteristics as recited in the appended claims, and madewith the use of known techniques of more obvious and immediate choice,such as the use of a direct pneumatic control or electromagneticactuators or means like a lever joint generally known as a toggle jointin the art, it has been observed that a number of problems tend to aarise in connection with the opening and closing, or clamping, of themoving half-mould, ie.:

the final closing and opening movement of the moving half-mould is anabrupt, not adequately slowed-down one, so that it may give rise toblows and clattering;

owing to the rapid wear-down of the mechanical organs and partsconcerned (it should be noted that these must be able to operate on acontmuous-duty basis over very long periods of time), the duration ofthe machine life is significantly affected, ie. reduced, thereby givingrise to immediate problems of planned maintenance and/or repair work;

the noise generated by the entire system controlling and actuating themovement of the moving half-mould is in general quite high and tends tofurther increase owing the the above cited wear-down effect;

since the moving half-mould must perform an alternating opening andclosing movement at a relatively high rate, vibrations are generatedwhich tend to be transferred to the entire structure of the plant, andthis has obviously a negative impact on the duration and the operationof the machine organs involved; furthermore, the final opening andclosing phase of the moulds is an extremely short and therefore stronglyaccelerated phase, and this of course contributes to an increased levelof the so induced vibrations; and

for such accelerations to be obtained, over-sized movement control anddriving organs must be used, but this fact not only has a negativeeffect on the level of the vibrations, but also, due to the greaterextent of wear-down caused, to the ability of ensuring the desiredprecision standards over adequately long periods of time.

SUMMARY OF THE INVENTION

Based on these considerations, it therefore is a main purpose of thepresent invention to provide a blow-moulding apparatus of a plant forproducing hollow bodies allowing for the productivity thereof to beincreased through an accelerated handling of both preforms and finishedcontainers, without incurring any of the afore mentioned drawbacks,which is capable of being easily implemented with the aid of readilyavailable techniques and means and therefore is reasonably low-cost,reliable and preferably capable of being integrated with a preformproduction stage arranged upstream.

BRIEF DESCRIPTION OF THE DRAWINGS

This above arm, along with further features of the present invention, isreached in a blow-moulding apparatus having the characteristics asrecited in the appended claims, and embodies itself in definite partsand arrangements of parts, as can be more readily understood from thedetailed description of a preferred embodiment that is given below byway of non-limiting example with reference to the accompanying drawings,in which:

FIG. 1 is a side vertical-section view of a pair of half-mouldsaccording to the present invention, shown at a closing angle enablingthe preforms to be introduced therein;

FIG. 2 is a side view similar to FIG. 1, however with the samehalf-moulds shown in a minimum opening position thereof enabling theblow-moulded container to be removed therefrom;

FIG. 3 is a schematic view of a path, as seen from above, followed by apreform to enter and to come out of a pair of half-moulds in a book-likeopen arrangement according to the prior air;

FIG. 4 is again a schematic view of the path, as seen from above,followed by a preform to enter and to come out of a pair of half-mouldsaccording to the present invention:

FIG. 5 is a vertical front view of the half-moulds in their openedstate, at the exact moment when the blow-moulded container starts to beremoved therefrom;

FIG. 6 is a schematic top view of the geometry and mutual arrangement ofa plurality of moulds according to the present invention;

FIG. 7 synthetically illustrates a comparison between two diagramsrepresenting on a horizontal scale the time requirements for carryingout a preform moulding phase according to the prior art and the presentinvention, respectively;

FIGS. 8 through 12 are views of positions of the moving half-mould, andthe related actuation organs, from a fully open to a fully closedposition thereof:

FIGS. 8A through 12A are schematic views of the locations on whichforces concentrate, as well as the axes along which the forces acting onthe actuation organs of FIGS. 8 through 12 concentrate;

FIG. 13 is a schematic view of the positions of fundamental pointvectors and force vectors acting on the actuation organs of FIG. 8, withthe mould in an open state; and

FIG. 14 is a diagrammatic view of position characteristics of the movinghalf-mould with respect to the position of an actuation pin from areference position thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A main feature of the present invention lies in the use of pairs ofhalf-moulds adapted to blow mould preforms 1 in view of converting theminto finished containers 7. The half-moulds are essentially arranged asillustrated in FIGS. 1, 2 and 6 showing, respectively, a schematic sidevertical-section view of a pair of half-moulds in a partially openstate, a schematic side vertical-section view of the same half-moulds inan almost fully open state, and a schematic top view of the arrangementof moulds 24, 25, 26 according to the present invention, in a fully openstate in the case of the moulds 24 and 25, and a fully closed state, inthe case of the mould 26.

On an outer periphery of a per se known rotating carousel 10 there areapplied a plurality of pairs of half-moulds, wherein

one of such half-moulds 2 is fixed and firmly joined to the carousel,and is further arranged on a vertical plane, with its respectivehalf-cavity facing outwardly and radially oriented with respect to thecarousel 10, and

the other half-mould 4 is movable with a rotary motion about an axis Xarranged on the horizontal plane and hinged on a rotation device (notshown) so that, when raised into its closed position, it is moved intocoupling exactly with the matching fixed half-mould 2 that is firmlyjoined to the carousel. In this way, therefore, the need actually arisesfor only the moving half-mould 4 to be actuated into closing andopening, since the other half-mould 2 is fixed and substantially firmlyjoined to the carousel.

In this connection, a look should be taken at the illustrationsappearing in FIGS. 3 and 4. In particular, the illustration in FIG. 3can be seen to show, in an extremely schematic manner, a top view of apath a followed by the preform, which is then moulded into a finishedcontainer, with respect to two half-moulds 21 and 22 according to theprior art (and therefore both movable) as shown in an open statethereof. From this Figure it can be readily noticed that path a mustinclude a deep sloping pattern in order to enable the preform to firstslide into the half-moulds and then move out therefrom as a finishedcontainer.

As compared with such a situation, the illustration appearing in FIG. 4shows, again in a schematic manner, a corresponding top view of a path bfollowed by the preform, which is then moulded into a finishedcontainer, with respect to the fixed half-mould 2 and the movinghalf-mould 4. Although sketched in a rather simplified form, thisillustration does not fail to immediately stress the point that the pathb of the preform runs along an arc of circumference without any apparentdiversion, or anyway a curvilinear trajectory without any point ofinflection that is likely to slow down the movement of thepreform/container along the path thereof or to add to the complexity ofthe construction of the motion control organs.

The line portions indicated at H, L, M, P and R in the diagram of FIG. 7respectively show the preform insertion time, the half-mould closingtime, the blow moulding time (dashed line), the half-mould re-openingtime, and the finished container removal time, according to theprior-art.

On the contrary, with the process according to the present invention,owing essentially to the closing phase of the moving half-mouldoccurring partially at the same time as the preform insertion phase, aswell as the opening phase of the same moving half-mould occurringpartially at the same time as the finished container removal phase, areduction in the overall cycle-time of the blow moulding tools can beobtained.

Since the above cited improvement allows for preform insertion phase H′to partially overlap closing phase L′ of the sole moving half-mould,such a time during which the two phases are carried out simultaneouslyis identified as time T⁰ which must necessarily be deducted from theoverall cycle time. Furthermore, after the related blow moulding phaseM′, which has necessarily an unaltered duration, the opening phase P′ ofthe moving half-mould is carried out. Even in this case, the possibilityexists for the subsequent removal phase R′ of the finished container tobe caused to start earlier, by a tune T′, before the mould is fullyopen, so that this partial overlapping of the opening phase P′ of themoving half-mould and the removal phase R′ of the finished blow-mouldedcontainer again brings about a further reduction in the overall cycletime by such period during which the phases are overlapping, ie. by theabove cited time T′.

In practice, the total cycle time is reduced from a value T_(x)indicated in FIG. 7 to a lower value T_(c), since T_(c)=T_(x)−T⁰−T¹.

Only a slight mention is made here of the fact that the actual blowmoulding time T_(s), which is also identified by a dashed portion inboth diagrams of FIG. 7, is common to and unaltered for both blowmoulding processes, so that it is not affected, ie. modified, by thepresent invention.

However, the advantages brought about by the present invention do notend here. In fact, a further improvement of the invention itself can beeasily obtained in the manner that is described below with particularreference to FIGS. 1 and 2.

Referring to FIG. 1, it can be noticed that the introduction of thepreforms in the blow moulding half-moulds, ie. the exclusive movement ofthe preforms towards the half-moulds, can be accomplished through just apartial opening of the moving half-mould 4, ie. when the opening angleis an angle that is smaller than the maximum opening angle. On thecontrary, this is not possible in those cases in which both half-mouldsare movable, owing to the particular kinematic mechanisms that would beneeded, as anyone skilled in the art is well aware of.

This furthermore leads to the advantage of the overall plant beingcapable of adjustment to the length of the preforms, since it can beeasily appreciated that shorter preforms require a smaller opening angleand, therefore, shorter mould insertion times. Similarly, as betterillustrated in FIG. 2, the movement for the removal of the finishedblow-moulded container can be started before the moving half-mould isfully opened, provided that the trajectory S of the lower edge of thesame container does not interfere with the moving half-mould.

A further advantageous improvement of the present invention lies inproviding an appropriately curved guide element 15, illustrated in FIGS.4 and 5, arranged in a stable manner in such position as to be able tointercept the path of the preform neck from the trajectory b, and toassist it in its movement of insertion in the respective cavity of thecorresponding fixed half-mould 2.

As far as the technical improvements in the organs controlling themovement of the moving half-mould are concerned, reference should bemade to FIGS. 8 through 12, as well as the corresponding schematicsappearing in FIGS. 8A through 12A. The latter can be seen tosymbolically represent the fundamental points of application of theaction and reaction forces on the organs of the plant, the vectorsrepresenting such forces, and the direction of action thereof.

From the illustrations in the above cited Figures it can be noticed thatthe actuation organs of the moving half-mould 4 comprise:

a first class lever provided with arms 52 and 53 separated by a fulcrumF1, whose power and resistance points are located at the extreme ends ofsaid two arms, ie. at P1 and R1, respectively;

a third class lever provided with respective arms 55 and 56, arespective fulcrum F2, and respective power and resistance points at P2and R2;

a rigid connecting member 54 that links the resistance point R1 of saidfirst class lever with the power point P2 of the third class lever, theresistance and power points being pivotally connected to the extremeends of the connecting member 54;

an actuating member 51 provided with two end portions, the first one ofwhich is connected to the power point P1 of the first class lever.

The fulcra F1 and F2 of the first class lever and the third class lever,respectively, are applied pivotally on respective distinct points of astructure 60 that is integral with or firmly joined to the fixedhalf-moulds. Furthermore, the moving half-mould 4 is applied on the arm56 of the third class lever opposite to the related fulcrum F2 withrespect to the corresponding power point P2.

The second extreme end 57 of said actuating member 51 is adapted to bemovably actuated by a moving member 58 on a plane that is orthogonal tothe axis of rotation of the fulcrum F1 of the first class lever.

The whole assembly of levers, connecting members and actuating membersis adapted to move, clearly in a synchronous and coherent manner, sinceeach moving member is linked to another member, between two respectiveextreme positions, in which one of such extreme positions corresponds tothe full-open position (FIGS. 8, 8A and 12) of the moving half-mould,whereas the other one of said extreme positions corresponds to thefull-closed position (FIG. 12, 12A and 16) of the same half-mould.

Referring now to FIG. 13, which illustrates the condition of the mouldassembly in its fully open position, it can be noticed that when thesecond extreme end 57 of the actuating member 51 is urged to startmoving in the direction in which the moving half-mould 4 is caused toclose, the vector V1 of the force transmitted from the point ofresistance R1 of the first class lever to the rigid connecting member 54has a component V2 in the direction of action on the connecting member,ie, along the straight line joining R1 with P2, wherein the componentV2, if considered as being applied on the point of power P2 of the thirdclass lever, indicated at V2,1 in the Figure, may be in turn broken downinto two mutually orthogonal components, one of which, ie, the oneindicated at V2,2 in the Figure, is oriented towards F2 and acts so asto only compress the related arm 55, with practically no effect at allwithin the overall geometry, whereas the other component V2,3 is radialwith respect to the arm 55 and therefore acts on the arm 56 supportingthe half-mould 4, in such a manner as to cause the third class lever torotate, thereby causing the moving half-mould to close.

As far as the spatial configuration and the possible components of theforce vectors, the lever arms and the other connecting/actuatingmembers, it has practically been found that the most effective andlogical arrangement thereof is obtained when all of them are provided ona same plane, in particular on the plane shown in the FIGS. 8 through12. However, as anyone skilled in the art is capable of readilyunderstanding, the vectors, members and components may also be arrangedthree-dimensionally, provided that they meet the pre-condition of theirprojections or components on a given, suitable plane reflecting thesubsequent conditions illustrated in the Figures.

FIGS. 9 through 11 illustrate subsequent dispositions of the wholeassembly of levers and connecting and actuating members, along with therespective vectors, corresponding to some subsequent positions of themoving half-mould 4 as it is moved into closing. They are, anyway,readily understandable by those skilled in the art, so that no furtherexplanation needs to be given here in this connection.

FIGS. 12 and 12A represent the situation when the moving half-mould isfully closed. This is a quite particular situation since, further torepresenting a kind of end-of-stroke point it also represents thecondition in which the “toggle effect” shows up in all of itseffectiveness. In other words, this is the condition in which theclamping force of the half-mould reaches its peak, ie, is maximized,while the angular displacement of the half-mould is at a minimum. Use isanyway made also of other means, further to this fact, in order toensure a fully stable clamping of the half-mould.

Reference should be made now to FIG. 12: the point of resistance R1 ofthe lever 52, 53 is in an articulated arrangement with respect to theconnecting member 54, so that the arm 53 and the connecting member 54are capable of rotating with respect to each other. However, a furtherrotation thereof beyond a pre-established position is prevented by thepresence of a mechanical or positive retainer (not shown) that reallyacts as a toggle, ie. enables two levers hinged on an extreme endthereof to rotate with respect to each other only up to a certain angleand not any further.

The geometric configurations and the dimensions of the various membersand components involved are so defined as to make sure that, when such alimit stop position is reached, this position also coincides with both

the full-closed condition of the moving half-mould against therespective fixed half-mould and

the particularly favourable condition created by the three geometricalsites identified by P2, R1 and F1 being aligned, as is shown in FIG.12A.

The advantageous character of such a circumstance has already beenhinted at above and lies essentially in the fact that, in the finalportion of the closing path covered by the moving half-mould, the forcethat is produced and can therefore be used to close and clamp thehalf-mould, is at its maximum, ie. reaches a peak. In this case in fact,as is most clearly shown in FIG. 14 illustrating the opening or closingangle of the moving half-mould in accordance with the progressivedisplacement of the moving member 58, or rolling pin, the mostfavourable condition is obtained in -new of making the best possible useof the so-called “toggle effect”, the condition being reached throughthe illustrated combination and association of the described leverages.In a more detailed manner, FIG. 14 can be noticed to emphasize how, incorrespondence of the portion of curve indicated at M, at a certainprogressive displacement of the device or rolling pin 58, whose scale inthe lower portion of the Figure is a linear one, a rotation is obtainedwith a progressively decreasing increment of the angle between themembers 54 and 55 until an angle of 0° is eventually reached between themembers 54 and 55 in correspondence of a value of approx. 1 in theabscissa.

The particular pattern followed by the curve in correspondence of theabove cited point M, which corresponds to the moving half-mould beingclosed, and also of the point H at the opposite end of the same curve,which corresponds to the full-open position of the half-mould, ensures amovement of the same half-mould with progressively slowed-downaccelerations and decelerations towards the respective end-of-strokepositions thereof, until practically a condition of zero acceleration isreached when the half-mould approaches the respective end-of-strokepositions thereof.

Such a moving pattern of the half-mould translates into a number ofsignificant practical advantages, ie. a noticeable reduction invibrations, the prevention of the moving half-mould from bumping whenmoving into its end-of-stroke positions, and the possibility for themoving device to be actuated with the help of simple, reliable andaccurate means that are furthermore durable, ie. well resistant towear-down since they are not subject to the action of “forces”.

This condition is further strengthened by the fact that, immediatelyupon the moving half-mould having so been moved into its fully closedposition, the same half-mould is automatically clamped in such aposition with the help of such supplementary external means as readilyconceivable by all those skilled in the art, the means being linked tothe pins 41, 42 that are firmly joined with the fixed half-mould and themoving half-mould, respectively.

It will of course be appreciated that when it is stated that thegeometrical sites identified by P2, R1 and F1 are aligned, as is shownin FIG. 12A, this is meant to be understood in the broadest sense of theword, since this is actually intended to mean that, in order to ensurethe desired “toggle effect”, it is sufficient for the axes of rotationof the pins centered on P2, R1 and F1 to be not only parallel, but alsoarranged on the same plane.

The continuous operation of the described assembly for alternatinglyopening and closing the moving half-mould can be obtained through acorresponding to-and-fro movement of the moving device or roiling pin58. Such a movement can be easily obtained by means of a continuouslyrotating cam device adapted to control the movement and the position ofthe rolling pin in full synchronization with all other devices,mechanisms and actuators that altogether ensure the various phases foropening the half-mould, introducing the preform, closing the half-mould,blow moulding the preform, opening the half-mould and simultaneousremoval of the finished container.

A further advantage of the present invention, as exemplified in theillustrated embodiment thereof, derives from the fact that if, as juststated above, the alternating to-and-fro movement of the moving deviceor rolling pin 58 is actuated by two rotating cams, preferably on thesame vertical axis of rotation of the carousel 10 in FIG. 6, the limitedweardown effect that unavoidably takes place between the actuatingsurfaces of the rotating cams and the rolling pin has only a verylimited impact on the opening and closing accuracy of the moulds. Thisfact brings about the remarkable benefit deriving from the possibilityfor the maintenance or re-adjustment of the cams and therewithassociated organs to be carried out at quite extended intervals, withoutincurring any loss in processing precision.

A confirmation of the fact that the weardown effect of the cams, andpossibly also of the associated rolling pin or moving device, has only avery limited impact on the precision of the end-of-stroke positions ofthe moving half-mould, can be simply obtained by again having a look atFIG. 14, in which it can in fact be observed that the condition actuallyoccurs in which, in front of a certainly non-negligible displacement,ie. oscillation of the rolling pin about the points M and H, the angleof rotation of the moving half-mould is almost nil and practicallynegligible. As a result, if such an oscillation is due to weardown, thispractically has no significant effect on the precision of theend-of-stroke positions of the moving half-mould.

What is claimed is:
 1. Apparatus for blow moulding hollow plastic bodiescomprising: a plurality of pairs of mutually joinable half-mouldscapable of being opened and closed, linked to an appropriate rotaryapparatus carrying said half-moulds, support devices for carryingpreforms corresponding to said half-moulds, a preform feeding mechanismadapted to supply an orderly sequence of preforms held at an appropriateblow-moulding temperature into the respective pairs of half-mouldsassociated to said rotary apparatus, which are to this purpose kept intheir opened position, a retrieval device adapted to remove the finishedcontainer from the respective pair of half-moulds after the openingthereof, an opening and closing mechanism adapted to close thehalf-moulds after the passage thereof through the position of thepreform feeding mechanism, and to open them before the passage thereofthrough the position of the finished-container removal mechanism,characterized in that said pairs of half-moulds are constituted by afixed half-mould and a moving half-mould that is capable of being openedfrom and closed against said fixed half-mould, said fixed half-mouldsbeing arranged in a substantially vertical position, and the respectivemoving half-mould being adapted to be closed by accomplishing asubstantially rotary movement about a horizontal axis of rotation,characterized in that said opening and closing mechanism of any of saidmoving half-moulds comprises: a first class lever and a third classlever, a structure firmly associated to said fixed half-moulds, aconnecting member that joins the point of resistance of said first classlever with the point of power of said third class lever, said resistanceand power points being pivotally connected to the extreme ends of saidconnecting member, an actuating member provided with two extreme ends,of which the first extreme end is connected to the power point of saidfirst class lever, the fulcra of said first class lever and said thirdclass lever being pivotally applied on respective distinct points ofsaid structure firmly associated to said fixed half-moulds, and saidmoving half mould being applied on the arm of said third class leverwhich is opposite to the related fulcrum with respect to thecorresponding power point.
 2. Apparatus according to claim 1,characterized in that the second extreme end of said actuating member isadapted to be forced by a moving device into displacing on an orthogonalplane with respect to the axis of rotation of the fulcrum of said firstclass lever.
 3. Apparatus according to claim 1, characterized in thatsaid levers and said connecting and actuating members are adapted tomove between two respective extreme positions, in which one of saidextreme positions corresponds to the full-open position of said movinghalf-mould, whereas the other of said extreme positions corresponds tothe full-closed position of said moving half-mould.
 4. Apparatusaccording to claim 3, characterized in that when said second extreme endof said actuating member is driven in the sense of starting the closingdisplacement of said moving half-mould from the full-open positionthereof, a vector of the force transmitted from said resistance point ofsaid first class lever to said connecting member has a component in thedirection of said connecting member which, when applied on to said powerpoint of said third class lever, has in turn a respective secondcomponent that is oriented so as to induce a rotation of said thirdclass lever in the closing direction of said moving half-mould. 5.Apparatus according to claim 1, characterized in that in said fullyclosed position of said moving half-mould, said power point and saidfulcrum of said third class lever, as well as said resistance point ofsaid first class lever are either aligned or the respective axes ofrotation are parallel and lie on the same plane.
 6. Apparatus accordingto claim 1, characterized in that said moving device is adapted to bedriven into alternatingly displacing between two extreme positionscorresponding to the conditions in which said moving half-mould is fullyopen and fully closed, respectively, by means of a cam device rotatingabout an axis that is orthogonal to the axes of rotation of said twolevers.
 7. Apparatus according to claim 1, characterized in that in saidfull-closed position thereof there is provided a retaining deviceadapted to prevent said moving half-mould from further rotating beyondsaid full-closed position.
 8. Apparatus according to claim 1,characterized in that selectively actuatable means are provided whichare adapted to prevent said moving half-mould from rotating back towardsthe open position from said full-closed position.
 9. Apparatus accordingto claim 1, characterized in that, in the position of maximum opening ofsaid moving half-mould, said power point of said first class lever isaligned with said second extreme portion of said actuating member andwith said moving member.
 10. Apparatus according to claim 9,characterized in that said moving member is allowed to be dragged alonga rectilenear translational movement only.
 11. Apparatus according toclaim 10, characterized in that said rectilenear translational movementis orthogonal to the direction of the alignment among: said power pointsaid second extreme portion of said actuating member and said movingmember, when said moving half-mould is in the position of maximumopening.
 12. Apparatus according to claim 9, characterized in that itcomprises two different toggle levers.
 13. Apparatus according to claim26, characterized in that one of said toggle levers is fully extendedwhen the moving half-mould is fully opened, and the other of said togglelevers is fully extended when the moving half-mould is fully closed. 14.Apparatus according to claim 10, characterized in that it comprises twodifferent toggle levers.
 15. Apparatus according to claim 11,characterized in that it comprises two different toggle levers. 16.Apparatus according to claim 14, characterized in that one of saidtoggle levers is fully extended when the moving half-mould is fullyopened, and the other of said toggle levers is fully extended when themoving half-mould is fully closed.
 17. Apparatus according to claim 15,characterized in that one of said toggle levers is fully extended whenthe moving half-mould is fully opened, and the other of said togglelever (53, R1, 54) is fully extended when the moving half-mould is fullyclosed.
 18. Apparatus according to claim 2, characterized in that saidlevers and said connecting and actuating members are adapted to movebetween two respective extreme positions, in which one of said extremepositions corresponds to the full-open position of said movinghalf-mould, whereas the other of said extreme positions corresponds tothe full-closed position of said moving half-mould.
 19. Apparatusaccording to claim 18, characterized in that when said second extremeend of said actuating member is driven in the sense of starting theclosing displacement of said moving half-mould from the full-openposition thereof, a vector of the force transmitted from said resistancepoint of said first class lever to said connecting member has acomponent in the direction of said connecting member which, when appliedon to said power point of said third class lever, has in turn arespective second component that is oriented so as to induce a rotationof said third class lever in the closing direction of said movinghalf-mould.